What is it ? The buffer is the part of the gun that locks the butt-stock to the receiver.

What does it do ? It serves as a recoil damper, a holder for the recoil spring, a mount for the butt-stock , and an actuator for the ejector.

Where does it go ?At the rear of the receiver. It locks into cams that are riveted to the inside of the receiver .
shown in this pic by the red arrows.

How does it attach ?it should slide into the receiver and twist 90 degrees to lock into two cams placed inside of the receiver at the rear. It is held in place from twisting loose by a small buffer catch on the bottom of the receiver.
^ above buffer latch group - attaches to bottom of receiver
V below rear of buffer were buttstock attaches , NOTE - larger notch on bottom for buttstock catch.

What are the different types ?Well , the obvious two are the original " MG42 type " that locks in with a counterclockwise motion, and the latter " MG3 type " designed to work with the MG3 recuperator( Recuperator sticky ) with the long tail. This latter style is designed to lock in with a clockwise spin.
less obvious are the differences in post war and war time buffers. they look identical to the eye but the war time buttstocks do not fit post war buffers correctly as the thread pitch or depth is slightly different.

shown in picture (buffer group) but not included in this list are buffer latch , roll pin and spring as these are related but mount to the bottom of the receiver.

How do i assemble it ? This buffer group picture shows the parts lay-ed out in order they reassemble.

What modifications are required to convert the buffer to work in the semi-auto SA42 ?some guns will require the buffer screw head to be drilled out for more clearance for the firing pin. Some members recommend grinding the nose cap into a tapered shape to ease its entering the bolt extension to strike the ejector button on the rear of the bolt.

What modifications are required to convert the MG42 Buffer to work with the MG3 recuperator ? a notch for the buffer latch will need to be cut into the other lobe (180 degrees out) of the cam locking area. Also the small notch on rear of the buffer will need to be cut for the buttstock locking latch to the same size as the big one.